Bioenergy. Tim Searchinger STEP Lecture November 6, 2017

Transcription

1 Bioenergy Tim Searchinger STEP Lecture November 6,

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3 EMISSIONS OF BIO-ELECTRICITY FROM HARVESTED WOOD Initial Committed Emissions: Emissions from unused cut wood (roots & residues) ~ 1/3 of total standing wood Smokestack emissions ~ 2.75 to 3 tons of CO 2 from wood for each 1 ton from natural gas or 1.5 tons compared to coal Upfront or committed short-term emissions are roughly 225% to 350% per kwh Subsequent 20 or 30 years Growth if harvested minus growth if unharvested, e.g., Harvest mid-age forest- probably lowers total growth for 10 years or more & little change after 30 for many forests Bottom line: probable large increase in emissions 3

4 Potential Energy from Total Annual Wood Harvests ( Average) European Union United States of America World Roundwood (Coniferous) (cubic meters) 281,991, ,664,423 1,134,700,239 Roundwood (NonConiferous) (cubic meters) 130,887, ,699,296 2,268,489,470 Wood Residues Used (cubic meters) 44,200,075 13,875, ,170,948 Oven-dry Roundwood in tonnes 1 184,352, ,751,809 1,652,781,791 Exajoules of Roundwood Primary Energy Consumption in Exajoules Percent Roundwood is of Primary Energy 5.2% 3.3% 6.4% Exajoules of residual wood Percent Wood Residuals is of Primary Energy 0.6% 0.1% 0.2% Percent Total Wood (roundwood plus residuals) of Primary Energy Consumption 5.8% 3.4% 6.7% 4

5 Existing Global Plant Harvests Have Transformed or Substantially Manipulated ~ 75% of all Vegetated Lands Courtesy IIASA 5

6 Global Land Use Demands By 2050 (without more bioenergy) 50-70% more crops 70%-90% more forage for livestock 20-70% more wood 6

7 Nearly all studies project that agricultural land will need to expand just to feed the world by Chart shows Future Cropland Projections from Different Models C. Schmitz et al. Agricultural Economics 45 (2014) Also: Bajzelj et. al., Nature CC (2014) Cropland Pasture Tilman et al. (2011) ~1 billion total addition agricultural land Searchinger/WRI

8 Additional Land Demands by 2050 > 120 million hectares of urban expansion by 2030 (Seto et al. PNAS 2012) 20-70% increased demand for wood Potential high pop.of 10.6 billion (UN) 8

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11 Solar conversion efficiencies Iowa corn Ethanol, % Most optimistic location future US switchgrass (DOE) (24 tdm/ha and 100 gallons/tonne) 0.35% Brazilian sugarcane ethanol, 0.2% PV 16% gross; 11% net 11

12 And average green is 87 to 1 12

13 Benefit bioenergy: Use land to produce plants to displace fossil emissions But Cost: Not using land for some other purpose

14 Benefit v. Cost of Using Even Surplus Land Ethanol at High Yields 1040 liters/hectare Savings from Displacing Petrol With No Land Use Change & No Production & Refining emissions ~3 tons of carbon per hectare for Ethanol Savings from Displacing Petrol with Production & Refining Emissions Equal to 50% of Petrol, e.g. optimistic view of maize ethanol from Iowa 1.5 tons of carbon per hectare Carbon Cost of Just Not Allowing Any Surplus Land to Regrow Forest ~3 4.5 tons of carbon per hectare (1040 liters/hectare: E.g. US Corn Ethanol (after deducting byproducts) or Cellulosic ethanol at 17 dry tons/ha/y and 379 liters per 14

15 And average green is 87 to 1 15

16 Plant growth and resulting biomass is nearly all used for food, timber & either sequestering or replenishing carbon storage so To provide benefits, biofuels must use or result in additional plant growth (or use waste)

17 Large Bioenergy Potential Studies Double Count Biomass and Carbon Most potential arable land IPCC 2001 chapter 8-1.3billion hectares and/or All forest growth in excess of harvest (Smeets 2008)and/or All abandoned cropland (Hoodwijk (2004) and/or Hundreds of millions of hectares of grazing or other land savannah (Fischer 2001; Smith 2007) Diversion of timber product demand elsewhere Recounts existing forest, forest re-growth, net terrestrial carbon sink, land counted for grazing 17

18 Gross terrestrial carbon sink (2.8) & ~1 Gt logging regrowth (slightly exceeds logging source) 18

19 Forest Regrowth on Abandoned Land is Critical to Lower Net Loss of Forests & Carbon FAO, Global forest land use change (2012) 19

20 Claimed Marginal Land is Misnomer Zomer et al. Ag Ecosystems (2008): Fig. 2. Global map of CDM- AR suitable land (dark green) within Non-Annex I countries (light yellow), as delineated by the land suitability analysis. A 30% crown cover density threshold was used to define forest, and protected areas are not included. Hoodgwijk et al. (2005) Cai et al., Figure 2 Searchinger 2017

21 Agribusiness Boom Threatens Key African Wildlife Migration (March 7, 2011) Converted Miombo Woodland Zambia 21

22 Wet Savannas Are Not Potential Low Carbon Sources of Biofuels Searchinger et al., Nature Climate Change (2015) 22

23 BOTH BIOMASS AND FOSSIL FUEL COMBUSTION EMIT CARBON DIOXIDE, POTENTIAL SAVINGS COME FROM PLANT UPTAKE 23

24 Credit for Plant Growth Explains Findings of Greenhouse Gas Benefits in LCAs EU JRC Source of fuel* Producing Feedstock (crude oil or crop) Refining Tailpipe Emissions Fermentation emissions Total GHGs & % Increase for Biofuel Without Plant Credit Credit for Plant Growth Total GHGs & % Savings for Biofuel Gasoline EU Ethanol (+96%) (-29%) Greenhouse gas emissions and sinks (CO 2 eqv.) per mega joule of fuel 24

25 BIOENERGY IS A FORM OF LAND-BASED CARBON OFFSET Land grows plants whether for bioenergy or not: * forest * food Only ADDITIONAL plant growth helps 25

26 Typical Understanding of Biofuels & GHGs Assumes direct changes are good CO 2 emisson CO 2 CO 2? But maybe Yeah! 26

27 Effect of switching from gasoline to biofuels grown on otherwise unproductive land Reduced atmospheric CO 2 through increased plant growth Unproductive land CO 2 emission New crop growth CO 2 emission Car, gasoline Gasoline Use CO 2 uptake Ethanol Use Car, ethanol 27

28 Using otherwise burned or decomposed crop residues for biofuels - Reduced emissions through reduced land sources CO 2 emission CO 2 emission CO 2 emission X Burning or decomposing crop residues Car, gasoline Reduced emissions from Residues Car, ethanol 28

29 Figure 2 - Direct effect of switching from gasoline to biofuels that use existing crops No change in emissions Crop growth CO 2 emission Crop growth CO 2 emission CO 2 uptake Gasoline Use Car, gasoline CO 2 uptake Ethanol Use Car, ethanol 29

30 Figure 3 - Indirect effect 1 of adopting ethanol Ethanol leads to less crop consumption for feed and food, which reduces CO 2 Crop growth CO 2 emission CO 2 emission Crop growth CO 2 emission CO 2 em. CO 2 uptake Car, gasoline Gasoline Use Livestock & human respiration, methane and wastes CO 2 uptake Car, ethanol Ethanol Use Reduced livestock & human respiration, methane and wastes (vertical arrows indicate carbon uptake and emissions) 30

31 Searchinger, Edwards et al., Do Biofuel Policies Seek to Cut Emissions by Cutting Food, Science (2015) Government Biofuel Models: 25% to 50% of Calories Diverted to Grain Ethanol are Not Replaced 31

32 Figure 5 Indirect effect 3 of adopting ethanol Ethanol leads to land use change, which increases crop growth, but sacrifices forest or grassland and probably causes net increase in CO 2 Crop growth CO 2 emission Crop growth CO 2 emission CO 2 emission Land conversion CO 2 uptake Gasoline Use Car, gasoline CO 2 uptake Car, ethanol Ethanol Use CO 2 uptake 32

33 Possible Carbon Costs of Land Alternative Use of Land Tropical seasonal forest (75% of Gibbs et al. 2008) Humid tropical savanna (75% of Gibbs et al. 2008) Existing temperate forests (conservative) Carbon opportunity cost of using land for bioenergy instead of alternative Implicit ILUC Cost for Bioenergy at High Yields ~5.5 tons/hectare/year ~163 gco2/mj ~3 tons C/hectare/year ~87 gco2/mj ~6-~8 tons/hectare gco2/mj 33

34 Figure 4 - Indirect effect 2 of adopting ethanol Ethanol leads to yield growth on existing farmland to replace diverted crops, absorbing more carbon and probably reducing CO 2 Crop growth CO 2 emission CO 2, N 2 0 CO 2 emission CO 2 uptake Gasoline Use Car, gasoline Increased yields absorb more carbon on the same land but may increase emissions from fertilizer use CO 2 uptake Ethanol Use Car, ethanol 34

35 Future yields overall will need to grow faster than historical rates to prevent new land conversion Kg/ha/year Source: Alexandratos, N., and J. Bruinsma World agriculture towards 2030/2050: The 2012 revision. Rome: FAO; ACE and WRI analysis. 35

36 One lesson: Bioenergy is the Economic Feedbacks Cannot Make Bioenergy More Efficient 36

37 Searchinger et al., Assessing the Carbon Efficiency of Land Use Change (In review) 37

38 Renewable Does Not Equal Carbon Free 38

39 IPCC Guidelines IPCC 2000 Land Use Report (p. 355): Because fossil fuel substitution is already rewarded by excluding emissions from the combustion of bioenergy, to avoid underreporting... any changes in biomass stocks on lands... resulting from the production of biofuels would need to be included in the accounts. 39

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41 IAMS THAT PREDICT LARGE QUANTITIES OF BECCS ARE THOUGHT EXPERIMENTS BASED ON ULTRA- LAND EFFICIENT WORLD Popp et al. Climatic Change (2014) Searchinger 2017

42 1 ton of CCS = 1 ton of CCS Searchinger 2017

43 Conditions for possible benefits from BECCS from land Elimination of fossil fuel emissions (or CCS could be used to the same effect on fossil emissions) Surplus global land Extremely high biomass yields (or reforestation is better option) Very high carbon capture rates (or benefits undermined by carbon escape and additional energy needs for CCS). Solar generation of carbon-based liquids, which is technically achievable at much higher efficiencies and using desert, is not practically available. Searchinger 2017

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45 Sum Up Highly land-inefficient Requires massive quantities of land & water for modest quantities of energy Land is not available because of rising food/timber & carbon storage demands Land always has high opportunity cost Nearly all analyses of bioenergy potential and GHG reductions double count biomass & carbon Others are thought experiments not predictions Solar is 100 times more efficient & can use unproductive land Stakes are high 45

46 A Challenge for Science Why the error? (Understanding? Hope?) How do you fix it? Who will fix it? 46